Pipe stdin, stdout, and stderr when executing commands through
gitopolis exec. This prevents commands from detecting a TTY and
stops them from launching pagers, prompts, or other interactive
features.

Commands now run in a non-interactive environment where:
- stdin is set to null (no input available)
- stdout/stderr are piped and streamed line-by-line to the terminal

This ensures git commands (and other CLI tools) won't pause for
pagers or prompts that would hang the execution.

Updated README.md to document the non-interactive behavior and its
implications:
- Git defaults to no-color (can re-enable with --color flag)
- SSH/GPG keys must be pre-loaded in ssh-agent
- Remote SSH hosts must be in known_hosts

Applied to both repo_exec() and repo_exec_oneline() functions on
both Unix and Windows platforms.

Prompts:
- any idea how to fix this [exec git log not turning off pager · Issue #230 · timabell/gitopolis](#230)
- in response to: isn't that going to cause problems for cmd in windows? maybe only change if for unix builds
- in response to: will empty string work? if so do that on all
- in response to: is there a better way to tell git (and other cli commands) that it's non-interactive
- in response to: can we make stdout not a tty?
- in response to: that doesn't work, git is still paging with less. also give me a command i can use to test what other apps would generically be like
- in response to: add a note to the readme that commands run with exec are not tty to avoid hanging due to prompts, note that git will then default to no-colour but it can be re-enabled with --color
- in response to: add to that that this means you'll have to have your ssh/gpg keys already loaded and unlocked in ssh-agent or similar, and that remote ssh ids will need to already be accepted

Fixes #230

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>